JP2008190482A - Compression ratio variable control system for flexible fuel engine - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To prevent knocking at a time of fuel change over in a variable compression ratio flexible fuel engine. <P>SOLUTION: This compression ratio variable control system variably controlling compression ratio of the engine capable of using gasoline containing alcohol, is provided with a first alcohol content detection means 42 provided in an exhaust gas passage 20 of the engine 100 and detecting alcohol content of gasoline used during engine operation, and a before-engine-stop alcohol content storage means storing alcohol content before engine stop detected by the first alcohol content detection means 42 when the engine is stopped. Compression ratio of the engine 100 is set to a higher compression ratio in the next engine operation as the alcohol content gets higher. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

  The present invention relates to a variable compression ratio control device for an FF engine.

  Conventionally, there has been known an engine (hereinafter referred to as “FF engine”) used in an automobile (Flexible Fuel Vehicle) capable of using ethanol mixed gasoline (hereinafter referred to as “alcohol fuel”) in which ethanol is mixed with gasoline which is an alternative fuel for gasoline. (For example, see Patent Documents 1 and 2).

The alcohol fuel is referred to as “E85 fuel (ethanol content 85%)” according to the ethanol content. A gasoline-only fuel that does not contain ethanol may also be referred to as “E0 fuel” in the same way, but hereinafter, alcohol fuel refers to an ethanol-mixed fuel, and gasoline fuel does not contain ethanol and is a 100% gasoline fuel. Shall be pointed to.
Japanese Utility Model Publication No. 4-134645 Japanese Utility Model Publication No. 5-066261

  Since alcohol fuel has a higher octane number than gasoline fuel, an engine using alcohol fuel can be operated at a high compression ratio. Therefore, the alcohol fuel engine can burn the fuel at a higher temperature than the gasoline engine, can increase the thermal efficiency, and can suppress the emission of NOx.

  However, in order to avoid knocking during operation with gasoline fuel, the conventional FF engine had to be operated with a low compression ratio in accordance with gasoline fuel even when operating with alcohol fuel.

  Therefore, an object of the present invention is to provide variable compression ratio control of an FF engine that can operate the engine at a compression ratio according to the fuel used.

  The present invention is a variable compression ratio control device that variably controls the compression ratio of an engine that can use alcohol-containing gasoline, and is provided in the exhaust passage of the engine and used in engine operation. First alcohol content rate detecting means for detecting the alcohol content before storing the engine, and the alcohol content rate storing means before stopping the engine that stores the alcohol content rate before stopping the engine detected by the first alcohol content rate detecting means. And the higher the alcohol content, the higher the compression ratio of the engine is set.

  According to the present invention, the engine can be operated at a compression ratio corresponding to the fuel used.

  Hereinafter, embodiments of the present invention will be described with reference to the drawings.

(First embodiment)
FIG. 1 is a schematic view of an FF engine 100 including a variable compression ratio mechanism 50 according to the first embodiment of the present invention.

  The FF engine 100 includes an intake passage 10 through which fresh air flows. The intake passage 10 has an intake manifold 11 that distributes fresh air to the cylinders 2a to 2d. The intake manifold 11 branches into branch pipes 11a to 11d corresponding to the number of cylinders. The intake manifold 11 is connected to the cylinder head of the FF engine 100. The tip of the injector 33 is inserted into the intake manifold 11.

  The fuel injected from the injector 33 is stored in the fuel tank 30. A fuel supply sensor 34 for detecting that a fuel supply gun has been inserted is provided at the fuel supply port 34 of the fuel tank 30. Thereby, it can be determined whether or not refueling has occurred. The fueling gun sensor 41 is a system in which circuit interruption occurs when the cap 36 of the fueling port 34 is removed, and can determine whether or not the fueling gun is inserted by turning on and off.

  The fuel in the fuel tank 30 is supplied to the fuel gallery 32 through the fuel pipe 31. Hereinafter, the total capacity of the fuel pipe 31 and the fuel gallery 32 is referred to as “gallery internal capacity Fg”. The gallery internal capacity Fg corresponds to the fuel mass in the pipe (fuel pipe 31, fuel gallery 32, etc.) extending from the fuel tank 30 to the injector 33. The fuel supplied to the fuel pipe 31 is prevented from returning to the fuel tank 30 even when the engine is stopped by an unillustrated reverse support valve or the like.

  The fuel supplied to the fuel gallery 32 is injected into the intake manifold 11 by injectors 33 a to 33 d arranged in series in the fuel gallery 32 for each cylinder 2. The fuel injected into the intake manifold 11 is mixed with fresh air flowing through the intake manifold 11 and sucked into the cylinder 2. The air-fuel mixture sucked into the cylinder 2 becomes combustion gas and is discharged into the exhaust passage 20.

  The exhaust passage 20 has an exhaust manifold 21 for collecting exhaust discharged from the cylinders 2a to 2d in one system. An air-fuel ratio sensor 42 is disposed in the exhaust passage 20 downstream of the exhaust manifold 21. The air-fuel ratio sensor 42 detects the exhaust air-fuel ratio based on the oxygen concentration in the exhaust.

  The variable compression ratio mechanism 50 is a mechanism that changes the compression ratio by changing the piston stroke. As such a mechanism, in the present embodiment, a multi-link type compression ratio variable mechanism which has been previously proposed by the applicant of the present invention and which is publicly known, for example, from Japanese Patent Laid-Open No. 2001-227367 is applied. Hereinafter, an outline of the FF engine 100 including the multi-link compression ratio variable mechanism will be described with reference to FIGS. 2 and 3.

  The FF engine 100 having a multi-link type compression ratio variable mechanism connects the piston 122 and the crankshaft 121 with two links (an upper link (first link) 111 and a lower link (second link) 112), and The control link (third link) 113 controls the lower link 112 to change the compression ratio.

  The upper link 111 has an upper end connected to the piston 122 via a piston pin 124 and a lower end connected to one end of the lower link 112 via a connection pin 125. The piston 122 receives the combustion pressure and reciprocates in the cylinder 2 of the cylinder block 123.

  The lower link 112 has one end connected to the upper link 111 via the connecting pin 125 and the other end connected to the control link 113 via the connecting pin 126. Further, the lower link 112 inserts the crankpin 121b of the crankshaft 121 into a substantially central connecting hole, and swings about the crankpin 121b as a central axis. The lower link 112 is divided into two left and right members. The crankshaft 121 includes a plurality of journals 121a and a crankpin 121b. The journal 121a is rotatably supported by the cylinder block 123 and the ladder frame 128. The crank pin 121b is eccentric from the journal 121a by a predetermined amount, and the lower link 112 is swingably connected thereto.

  The control link 113 is connected to the lower link 112 via a connecting pin 126. The control link 113 is connected to the control shaft 114 at the other end via a connecting pin 127. The control link 113 swings around the connecting pin 127. A gear is formed on the control shaft 114, and the gear meshes with a pinion 132 provided on the rotation shaft 133 of the actuator 131. The control shaft 114 is rotated by the actuator 131, and the connecting pin 127 moves.

  FIG. 3 is a diagram for explaining a compression ratio changing method by the FF engine 100 having a multi-link variable compression ratio mechanism.

  The FF engine 100 including the multi-link variable compression ratio mechanism can change the compression ratio by rotating the control shaft 114 and changing the position of the connecting pin 127 by the controller 40 controlling the actuator 131. For example, as shown in FIGS. 3 (A) and 3 (C), when the connecting pin 127 is set to the position P, the top dead center position (TDC) is increased and a high compression ratio is obtained.

  As shown in FIGS. 3B and 3C, when the connecting pin 127 is moved to the position Q, the control link 113 is pushed upward, and the position of the connecting pin 126 is raised. As a result, the lower link 112 rotates counterclockwise about the crank pin 121b, the connecting pin 125 is lowered, and the position of the piston 122 at the piston top dead center (TDC) is lowered. Therefore, the compression ratio becomes a low compression ratio.

  By the way, since alcohol fuel has a higher octane number than gasoline fuel, the compression ratio can be increased. However, since the normal FF engine cannot change the compression ratio, in order to avoid knocking when operating with gasoline fuel, it must be operated with a low compression ratio that matches the gasoline fuel even when using alcohol fuel. It was.

  On the other hand, in the FF engine of the present invention, the cylinder volume is adjusted so as to be a low compression ratio in the case of gasoline fuel, and the cylinder volume is adjusted so as to be a high compression ratio in the case of alcohol fuel. Can do. As a result, combustion can be performed at an optimum compression ratio for both gasoline fuel and alcohol fuel.

  Therefore, in the present embodiment, based on the detection signal (exhaust air / fuel ratio) of the air / fuel ratio sensor 42, the controller 40 determines whether the fuel after refueling is gasoline fuel or alcohol fuel. In the case of alcohol fuel, there is a characteristic that the air-fuel ratio at the same fuel amount is leaner than in the case of gasoline fuel, so the controller 40 determines that it is alcohol fuel if the exhaust air-fuel ratio is lean, Otherwise, it is determined as gasoline fuel. And the controller 40 controls the compression ratio variable mechanism 50 so that it may become an optimal compression ratio according to the determined fuel at the time of engine starting. The controller 40 is composed of a microcomputer provided with a CPU, ROM, RAM, nonvolatile memory, and the like. A detection signal from an air flow meter 43 that detects the intake air flow rate of the engine 100 is input to the controller 40.

  Hereinafter, referring to FIG. 4 to FIG. 8, in order to control the compression ratio variable mechanism 50 so as to obtain an optimum compression ratio according to the fuel used, the controller 40 executes from the time of engine stop to the time of engine restart. Processing to be performed will be described.

  FIG. 4 is a flowchart for explaining processing executed by the controller 40.

  In step S11, the controller 40 determines whether or not the key switch has been switched from the ACC state to the OFF state. When the controller 40 is switched from ACC to OFF, the process proceeds to step S12. Otherwise, the process proceeds to step S13.

  In step S12, the controller 40 performs an engine stop process. Specific contents will be described later with reference to FIG.

  In step S13, the controller 40 determines whether or not the key switch remains in an OFF state. If the key switch remains in the OFF state, the controller 40 proceeds to step S14. Otherwise, the process proceeds to step S15.

  In step S14, the controller 40 performs an engine stop process. Specific contents will be described later with reference to FIG.

  In step S15, the controller 40 determines whether or not the key switch has been switched from the OFF state to the ACC state. When the key switch is switched from OFF to ACC, the controller 40 proceeds to step S16. Otherwise, the process proceeds to step S17.

  In step S16, the controller 40 performs engine startup processing. Specific contents will be described later with reference to FIG.

  In step S <b> 17, the controller 40 calculates a fuel amount (hereinafter referred to as “fuel consumption amount”) Fc that has been consumed since the last refueling. The controller 40 detects the fuel consumption amount Fc by the following formula while the engine 100 is operating.

  This will be described. The controller 40 obtains the fuel consumption amount ΔFc per unit time from the intake air amount Qa to the combustion chamber per unit time and the air-fuel ratio AFR during the operation of the engine 100. By setting the unit time equal to the processing calculation period in advance, ΔFc becomes the fuel consumption during the period from the previous process to the current process. Then, the controller 40 detects the fuel consumption (integrated amount) Fc by adding the fuel consumption amount ΔFc per unit time obtained in the current process to the previous value Fcz of the fuel consumption stored in the nonvolatile memory. To do.

  FIG. 5 is a flowchart showing the engine stop process.

  In step S121, the controller 40 stores the detection signal (hereinafter referred to as “air-fuel ratio backup value”) AFb of the air-fuel ratio sensor 42 when the engine is stopped in the nonvolatile memory. This is because the controller 40 controls the variable compression ratio mechanism 50 based on the air-fuel ratio backup value AFb in principle when the engine is restarted.

  FIG. 6 is a flowchart showing processing during engine stop.

  In step S141, the controller 40 determines whether or not a predetermined time has elapsed after the key switch has changed from the ACC state to the OFF state. If the predetermined time has not elapsed after the key switch is switched from ACC to OFF, the controller 40 proceeds to step S142. Otherwise, the process proceeds to step S143.

  In step S142, the controller 40 performs a sleep transition process.

  In step S143, the controller 40 determines whether or not a predetermined time has elapsed after resetting the fuel consumption amount Fc to zero. If the predetermined time has elapsed after the reset of the fuel consumption length Fc, the controller 40 proceeds to step S144. Otherwise, the current process is terminated.

  In step S144, the controller 40 performs a sleep process. During the sleep process, the controller 40 operates with low power consumption.

  In step S145, the controller 40 determines whether or not the refueling determination flag has become 1. Here, the refueling determination flag is a flag that switches from 0 to 1 according to the detection signal of the refueling gun sensor 41 when refueling. When the refueling determination flag is 0, the controller 40 ends the current process. If refueling is performed and the refueling determination flag is 1, the controller 40 proceeds to step S146.

  In step S146, the controller 40 is activated from the sleep process.

  In step S147, the controller 40 resets the fuel consumption amount Fc to zero. As described above, the fuel consumption amount Fc is the amount of fuel consumed from the last refueling to the present. Therefore, when fueling is performed, the fuel consumption amount Fc is reset to zero.

  FIG. 7 is a flowchart showing the engine starting process.

  In step S161, the controller 40 is activated from the sleep process.

  In step S162, the controller 40 determines whether or not the fuel consumption amount Fc exceeds the gallery capacity Fg. This is because it can be determined that the fuel in the pipe from the fuel tank 30 to the injector 33 is filled with the fuel after refueling if the fuel consumption Fc after refueling exceeds the in-gallery capacity Fg. It is. The controller 40 proceeds to step S163 if the fuel consumption amount Fc exceeds the in-gallery capacity Fg, and proceeds to step S165 if not exceeded.

  In step S163, the controller 40 determines whether the fuel is gasoline fuel or alcohol fuel from the air-fuel ratio backup value AFb stored in the nonvolatile memory when the engine is stopped.

  In step S164, the controller 40 controls the variable compression ratio mechanism 50 so as to obtain an optimal compression ratio according to the determined fuel.

  In step S165, the controller 40 controls the compression ratio variable mechanism 50 so that the compression ratio (low compression ratio) when the fuel is gasoline fuel is obtained.

  FIG. 8 is a time chart showing the operation of processing executed by the controller 40 from when the engine is stopped to when it is stopped. In addition, in order to clarify the correspondence with the flowchart, description will be made with the step number of the flowchart.

  When the key switch is operated from ON to OFF at time t1 (FIG. 8A; S11), the controller 40 enters the sleep transition state (FIG. 8D; S142), and the engine speed and the air-fuel ratio sensor 42 are turned on. Both outputs are 0 (FIGS. 8B and 8C). Further, the controller 40 stores the output value of the air-fuel ratio sensor 42 at time t1 in the nonvolatile memory as the air-fuel ratio backup value AFb (S121).

  At time t2, the controller 40 enters a sleep state (FIG. 8D; S144).

  When refueling is performed at time t3 in the sleep state and the refueling determination flag is switched from 0 to 1 (FIG. 8E; S145), the controller 40 is activated (FIG. 8D; S146), and the fuel consumption amount Fc is reset to zero (FIG. 8 (F); S147).

  When the controller 40 resets the fuel consumption amount Fc to zero, the controller 40 enters the sleep state again at time t4 after a predetermined time has elapsed (FIG. 8D; S144, S145).

8 (D) to 8 (F), the operation of the detection signal of the controller 40 and the fueling gun sensor 41 and the fuel consumption amount Fc when fueling is not performed is indicated by broken lines. The operations in FIGS. 8A to 8C are the same as when refueling is performed. As shown in FIG. 8, if refueling is not performed, the controller 40 remains in the sleep state (FIG. (E)). Therefore, the fuel consumption amount Fc is not reset, and after the engine is restarted, the fuel amount consumed by the engine operation after the engine restart is added to the previous fuel consumption amount (FIG. 8F). .

  9 and 10 are time charts showing the operation of the process executed by the controller 40 when the engine is started.

  First, a description will be given with reference to FIG. FIG. 9 is a time chart in the case where the fuel consumption amount Fc from the previous refueling to the present is smaller than the gallery internal capacity Fg.

  When the key switch is operated from OFF to ACC at time t5 (FIG. 9A; S15), the controller 40 becomes active at time t6 (FIG. 9B; S161).

  When the controller 40 becomes active at time t6, the controller 40 compares the fuel consumption Fc with the gallery capacity Fg (S162).

  At this time, if Fca <Fg (FIG. 9C), the low compression ratio request flag is switched from 0 to 1 (FIG. 9D). If Fca <Fg, the fuel before refueling remains in the piping from the fuel tank 30 to the injector 33. Naturally, the air-fuel ratio backup value AFb is the value of fuel before refueling. Therefore, for example, when the fuel before refueling is alcohol fuel and the fuel after refueling is gasoline fuel, if the compression ratio of the compression ratio variable mechanism 50 is set to a high compression ratio based on the air-fuel ratio backup value AFb, the engine restarts. There is a possibility that the fuel changes during the subsequent driving and knocking occurs. Therefore, if Fca <Fg, the low compression ratio request flag is switched from 0 to 1, and the compression ratio of the compression ratio variable mechanism 50 is set to the low compression ratio regardless of the fuel.

  When the low compression ratio request flag is 1, at time t7, the controller 40 instructs the compression ratio to become the low compression ratio (FIG. 9E; S165).

  When the compression ratio is controlled to a predetermined compression ratio at time t8 (FIG. 9F), the starter motor is started at time t9 (FIG. 9A). As a result, the engine rotation speed increases and reaches the idle rotation speed (FIG. 9G).

  Next, a description will be given with reference to FIG. FIG. 10 is a time chart in the case where the fuel consumption amount Fc from the last refueling to the present is greater than the gallery capacity Fg.

  The difference from the time chart of FIG. 9 will be mainly described. Since Fca> Fg (FIG. 10C), the low compression ratio request flag remains 0 (FIG. 10D).

  If Fca> Fg, the piping from the fuel tank 30 to the injector 33 is completely filled with fuel after refueling. Therefore, there is no problem that the fuel is switched during the travel after the engine restarts and knocking occurs. Therefore, when Fca> Fg, when the engine is restarted, the compression ratio of the compression ratio variable mechanism 50 is set based on the air-fuel ratio backup value AFb stored in the nonvolatile memory when the engine is stopped.

  That is, when the low compression ratio request flag is 0, at time t7, the controller 40 instructs the compression ratio of the compression ratio variable mechanism 50 based on the air-fuel ratio backup value AFb stored in the nonvolatile memory when the engine is stopped (FIG. 10 (E); S304).

  At time t8, the compression ratio is controlled to a predetermined compression ratio (FIG. 10 (F)).

  As described above, the FF engine 100 having the variable compression ratio mechanism 50 needs to determine whether the fuel supplied is alcohol fuel or gasoline fuel on the premise of controlling the compression ratio. Therefore, in the present embodiment, an air-fuel ratio sensor 42 is provided in the exhaust passage 20 to make a determination from the air-fuel ratio of the exhaust.

  At this time, when it is determined only by the air-fuel ratio sensor 42 provided in the exhaust passage 20 whether the fuel supplied is alcohol fuel or gasoline fuel, the determination is made after the engine is restarted after fueling. Only when the fuel combustion gas is detected by the air-fuel ratio sensor 42 is it possible.

  Therefore, in the present embodiment, a fuel supply gun sensor 41 is provided as a fuel supply determination unit, and the fuel consumption amount Fc from the previous fuel supply to the present is calculated. Then, the fuel consumption Fc is compared with the gallery internal capacity Fg corresponding to the fuel mass in the pipe from the fuel tank 30 to the injector 33.

  As a result of comparison, when the fuel consumption Fc from the last refueling to the present is larger than the gallery internal capacity Fg (Fca> Fg), all the fuel after refueling in the pipe from the fuel tank 30 to the injector 33 is obtained. Can be determined to be satisfied. Therefore, in this case, the compression ratio of the compression ratio variable mechanism 50 is set based on the air-fuel ratio backup value AFb stored in the nonvolatile memory when the engine 100 is restarted.

  On the other hand, as a result of comparison, if the fuel consumption Fc from the last refueling to the present is less than the gallery internal capacity Fg (Fca <Fg), the pre-refueling in the pipe from the fuel tank 30 to the injector 33 is performed. It can be determined that fuel remains. Therefore, in this case, if the compression ratio of the compression ratio variable mechanism 50 is set based on the air-fuel ratio backup value AFb stored in the nonvolatile memory when the engine 100 is restarted, the compression ratio suitable for the fuel before refueling is set. End up. That is, the compression ratio set when engine 100 is restarted does not become a compression ratio suitable for fuel after refueling.

  Therefore, for example, when the fuel supplied with the alcohol fuel before the refueling is the gasoline fuel, the alcohol content of the fuel in the fuel tank 30 decreases. Therefore, if the compression ratio of the variable compression ratio mechanism is set to a high compression ratio based on the air-fuel ratio backup value AFb, there is a possibility that knocking may occur due to switching to a fuel with a low alcohol content during running after the engine is restarted. is there.

  Therefore, when Fca <Fg, the compression ratio of the compression ratio variable mechanism 50 is set to a low compression ratio suitable for gasoline fuel regardless of the fuel determined based on the air-fuel ratio backup value AFb. Thereby, even if the alcohol fuel with a high alcohol content is switched to the alcohol fuel or the gasoline fuel with a low alcohol content during the engine operation, the occurrence of knocking can be prevented.

  Thus, according to the present embodiment, the engine 100 can be operated at the compression ratio corresponding to the fuel by the variable compression ratio mechanism 50. Further, when the fuel is switched during engine operation, knocking that occurs particularly when the fuel is switched from alcohol fuel to gasoline fuel can be avoided.

(Second Embodiment)
Next, a second embodiment of the present invention will be described with reference to FIG. This embodiment is different from the first embodiment in that it has two alcohol concentration detection means, that is, an air-fuel ratio sensor 42 and an alcohol sensor 44. Hereinafter, the difference will be mainly described. In the following embodiments, the same reference numerals are used for portions that perform the same functions as those in the first embodiment described above, and repeated descriptions are omitted as appropriate.

  FIG. 11 is a schematic view of an FF engine 200 provided with a variable compression ratio mechanism 50 according to the second embodiment of the present invention.

  The FF engine 200 has basically the same configuration as that of the FF engine 100 according to the first embodiment, but is different in that it has an alcohol sensor 44 and does not have an oil supply gun sensor (oil supply determination means).

  The alcohol sensor 44 is provided at the base end (the injector 33d side) of the fuel gallery 32. The alcohol sensor 44 outputs an electrical signal corresponding to the alcohol concentration in the fuel to the controller 40.

  Next, processing executed by the controller 40 when the engine is stopped and when the engine is started according to the second embodiment of the present invention will be described with reference to FIGS.

  FIG. 12 is a flowchart for explaining processing executed by the controller 40. In FIG. 12, the same reference numerals are given to the steps for performing the same processing as in FIG.

  In step S21, the controller 40 performs an engine stop process. Specific contents will be described later with reference to FIG.

  In step S22, the controller 40 determines whether or not the key switch has been switched from the OFF state to the ACC state. When the controller 40 is switched, the process proceeds to step S23. Otherwise, the process proceeds to step S15.

  In step S23, the controller 40 performs an engine start start process. Specific contents will be described later with reference to FIG.

  In step S24, the controller 40 determines whether or not the key switch is in an ON state.

  In step S25, the controller 40 performs an engine start process. Specific contents will be described later with reference to FIG.

  FIG. 13 is a flowchart showing the engine stop process.

  In step S211, the controller 40 stores the air-fuel ratio backup value AFb in the nonvolatile memory.

  In step S212, the controller 40 stores the change rate (hereinafter referred to as “alcohol sensor output change rate”) ALrc of the output signal (hereinafter referred to as “alcohol sensor output value”) ALrc of the alcohol sensor 44 for several seconds before the engine is stopped in the nonvolatile memory. To do.

  In step S213, the controller 40 is turned off.

  FIG. 14 is a flowchart showing an engine start start process.

  In step S231, the controller 40 determines whether or not the fuel determined based on the air-fuel ratio backup value AFb is alcohol fuel. If the determined fuel is alcohol fuel, the controller 40 proceeds to step S232, and if it is gasoline fuel, the controller 40 proceeds to step S235.

  In step S232, the controller 40 determines whether or not the fuel determined based on the alcohol sensor output value AL is alcohol fuel. If the determined fuel is alcohol fuel, the controller 40 proceeds to step S233. If the determined fuel is gasoline fuel, the controller 40 proceeds to step S234.

  That is, if both the fuel used when the engine is stopped and the fuel in the fuel gallery 32 are alcohol fuel, the controller 40 proceeds to step S233. If the fuel used when the engine is stopped is alcohol fuel and the fuel in the fuel gallery 32 is gasoline fuel, the controller 40 proceeds to step S234.

  In step S233, the controller 40 controls the compression ratio variable mechanism 50 to a high compression ratio suitable for alcohol fuel.

  In step S234, the controller 40 controls the variable compression ratio mechanism 50 so as to obtain a low compression ratio suitable for gasoline fuel.

  In step S235, the controller 40 controls the variable compression ratio mechanism 50 so as to obtain a low compression ratio suitable for gasoline fuel.

  In step S236, the controller 40 determines whether or not the fuel determined based on the alcohol sensor output value AL is alcohol fuel. If the determined fuel is alcohol fuel, the controller 40 proceeds to step S237. If the determined fuel is gasoline fuel, the controller 40 ends the current process.

  That is, if the fuel used when the engine is stopped is gasoline fuel and the fuel in the fuel gallery 32 is alcohol fuel, the controller 40 proceeds to step S237. If the fuel used when the engine is stopped and the fuel in the fuel gallery 32 are both gasoline fuel, the controller 40 ends the current process.

  In step S237, the controller 40 sets a high compression ratio request flag to 1.

  FIG. 15 is a flowchart showing the engine start process.

  In step S251, the controller 40 determines whether or not the compression ratio change by the compression ratio variable mechanism 50 has been completed. If the change of the compression ratio has been completed, the controller 40 proceeds to step S252. Otherwise, the current process is terminated.

  In step S252, the controller 40 starts the starter motor.

  In step S253, the controller 40 determines whether or not the high compression ratio request flag is set to 1. If the high compression ratio request flag is not set to 1, the controller 40 ends the current process, and if it is set, proceeds to step S254.

  In step S254, the controller 40 determines whether or not the elapsed time since the high compression ratio request flag is set to 1 is equal to or longer than the in-gallery fuel consumption time T1. If the elapsed time is equal to or longer than the fuel consumption time T1 in the gallery, the controller 40 proceeds to step S255. Otherwise, the current process is terminated.

  The controller 40 detects the fuel consumption time T1 in the gallery using the following formula. The fuel consumption time T1 in the gallery is the time taken to consume the gasoline fuel remaining in the fuel gallery 32.

  This will be described. The time required to consume the fuel in the fuel gallery 32 is calculated by dividing the capacity (fuel mass in the fuel gallery 32) Ffg of the fuel gallery 32 by the fuel consumption amount ΔFc per unit time. In order to consume the gasoline fuel remaining in the fuel gallery 32 by multiplying the time taken to consume the fuel in the fuel gallery 32 by a coefficient indicating the proportion of gasoline fuel remaining in the fuel gallery 32. Such time (fuel consumption time in the gallery) T1 can be calculated.

  F1 is a function for calculating a coefficient indicating the proportion of gasoline fuel remaining in the fuel gallery 32. By substituting the alcohol sensor output change rate ALrc into the function f1, a coefficient indicating the ratio of gasoline fuel within the range of 0 to 1 is calculated. When f1 = 1, the fuel gallery 32 is filled with gasoline fuel. When f1 = 0.5, half of the fuel gallery 32 is filled with gasoline fuel. Specifically, the front end of the fuel gallery 32 is filled with the gasoline fuel before refueling, and the alcohol fuel fed at the base end is filled.

  In step S255, the controller 40 controls the variable compression ratio mechanism 50 so that the compression ratio is suitable for alcohol fuel.

  According to the embodiment described above, the compression ratio variable mechanism 50 is controlled by comparing the fuel determined based on the air-fuel ratio backup value AFb and the fuel determined based on the alcohol sensor output value AL. Specifically, when both of the determined fuels are alcohol fuels (Yes in step S231 and Yes in step S232), the compression ratio variable mechanism 50 is controlled to a high compression ratio. When either one of the fuels is gasoline fuel (No in step S231 or No in step S232), the variable compression ratio mechanism 50 is controlled to a low compression ratio.

  At this time, in particular, when the air-fuel ratio sensor 42 detects gasoline fuel (No in step S231) and the alcohol sensor 44 detects alcohol fuel (Yes in step S236), the gasoline fuel is placed at the tip of the fuel gallery 32. Is satisfied, and the base end is filled with alcohol fuel. In this case, there is a high possibility that the fuel is switched from gasoline fuel to alcohol fuel during operation after the engine is started. However, even after the fuel is switched from gasoline fuel to alcohol fuel, if the engine is operated with a compression ratio suitable for gasoline fuel, effects specific to the FF engine such as reduction of exhaust NOx cannot be sufficiently obtained.

  Therefore, in the present embodiment, a time (fuel consumption time in the gallery) T1 required to consume the gasoline fuel remaining in the fuel gallery 32 is calculated, and after the time T1 has elapsed, the compression ratio variable mechanism 50 is suitable for alcohol fuel. Control to achieve a compression ratio.

  Thereby, when the fuel is switched from gasoline fuel to alcohol fuel, it is possible to operate at a high compression ratio. Therefore, fuel efficiency can be increased and NOx emission can be suppressed.

  Further, when the air-fuel ratio sensor 42 detects alcohol fuel (Yes in step S231) and the alcohol sensor 44 detects gasoline fuel (No in step S236), the tip of the fuel gallery 32 (injector 33a side) is detected. This is when the alcohol fuel is filled and the gasoline fuel is filled at the base end (injector 33d side). In this case, there is a high possibility that the fuel is switched from alcohol fuel to gasoline fuel during operation after engine startup. Therefore, if the variable compression ratio mechanism 50 is controlled so as to have a high compression ratio suitable for alcohol fuel, knocking may occur after the fuel is switched, which may affect the durability of the engine.

  Therefore, in the present embodiment, when the air-fuel ratio sensor 42 detects alcohol fuel and the alcohol sensor 44 detects gasoline fuel, the compression ratio variable mechanism 50 is set to a low compression ratio suitable for gasoline fuel in advance. Control.

  Thereby, even if the fuel is switched from alcohol fuel to gasoline fuel during engine operation, knocking can be prevented.

(Third embodiment)
Next, a third embodiment of the present invention will be described with reference to FIGS. The third embodiment of the present invention has the same configuration as the second embodiment, but in the engine start start process and the engine start process, the air-fuel ratio sensor 42 detects alcohol fuel and the alcohol sensor 44 detects gasoline fuel. The control of the compression ratio variable mechanism 50 when doing so is different from the second embodiment. Hereinafter, the difference will be mainly described.

  FIG. 16 is a flowchart showing an engine start start process. In FIG. 16, the same reference numerals are given to the steps for performing the same processing as in FIG.

  In step S331, the controller 40 controls the compression ratio variable mechanism 50 to a high compression ratio suitable for alcohol fuel.

  In step S332, the controller 40 sets a low compression ratio request flag to 1.

  FIG. 17 is a flowchart showing an engine start start process. In FIG. 17, steps that perform the same processing as in FIG. 15 are given the same reference numerals, and redundant descriptions are omitted.

  In step S351, the controller 40 determines whether or not the low compression ratio request flag is set to 1. If the low compression ratio request flag is not set to 1, the controller 40 ends the current process, and if it is set, the process proceeds to step S352.

  In step S352, the controller 40 determines whether or not the elapsed time since the low compression ratio request flag is set to 1 is equal to or longer than the in-gallery fuel consumption time T2. If the elapsed time is equal to or longer than the fuel consumption time T2 in the gallery, the controller 40 proceeds to step S353. Otherwise, the current process is terminated.

  As in the second embodiment, the controller 40 detects the fuel consumption time T2 in the gallery using the following equation. The fuel consumption time T2 in the gallery is a time taken to consume the alcohol fuel remaining in the fuel gallery 32.

  By substituting the alcohol sensor output change rate ALrc into the function f2, a coefficient indicating the proportion of gasoline fuel within the range of 0 to 1 is calculated. The fuel consumption time T2 in the gallery is calculated by taking the time taken to consume the fuel in the fuel gallery 32.

  According to the present embodiment described above, in addition to the effects of the second embodiment, since it is possible to operate at a high compression ratio until immediately before switching from alcohol fuel to gasoline fuel, the fuel efficiency can be further increased. Further, since the engine is not operated at a low compression ratio when the alcohol fuel is used, the emission of NOx can be further suppressed, and the deterioration of emission and exhaust odor can be prevented.

  Note that the present invention is not limited to the above-described embodiment, and it is obvious that various modifications can be made within the scope of the technical idea.

  For example, in this embodiment, a multi-link compression ratio variable mechanism is used as the compression ratio variable mechanism, but any known mechanism may be used as the compression ratio variable mechanism. For example, a variable valve timing control system (VTC) that changes the compression ratio by changing the amount of air taken into the cylinder by changing the opening / closing timing of the intake valve may be used. It is also possible to use a variable valve event and lift control system (VEL) that changes the compression ratio by changing the amount of air taken into the cylinder by changing the valve opening engine of the intake valve. Good.

  In the first embodiment, the fuel consumption amount is estimated from the intake air amount into the combustion chamber of the engine and the air-fuel ratio. However, the fuel consumption amount is determined in advance by experiments or the like from the engine rotation speed in consideration of the valve opening time of the injector. It may be estimated from a map or the like.

  Further, although the fuel switching is determined from the fuel consumption Fc and the gallery capacity Fg, it may be determined that the fuel has been switched if a predetermined time has elapsed after refueling.

  In the second and third embodiments, the controller 40 started the process at the time of engine start when the key switch is in the ACC state, but the signal of the key insertion detection switch that detects the key-in signal from the key box is started. You may start the process at the time of engine starting with a detection. As a result, processing can be started at an earlier time than when the key switch enters the ACC state, that is, together with the key-in signal.

It is the schematic of FF engine provided with the compression ratio variable mechanism by 1st Embodiment of this invention. It is a figure explaining FF engine provided with the multiple link type compression ratio variable mechanism. It is a figure explaining the compression ratio change method by FF engine provided with the multi-link type variable compression ratio mechanism. It is a flowchart explaining the process which the controller 40 performs. It is a flowchart which shows a process at the time of an engine stop. It is a flowchart which shows a process during engine stop. It is a flowchart which shows a process at the time of engine starting. It is a time chart which shows the operation | movement of the process performed with the controller 40 from the time of stopping an engine to a stop. It is a time chart when the fuel consumption Fc from the time of the last refueling to the present is smaller than the gallery capacity Fg. It is a time chart when the fuel consumption Fc from the time of the last refueling to the present is larger than the gallery capacity Fg. It is the schematic of FF engine 200 provided with compression ratio variable mechanism 50 by a 2nd embodiment of the present invention. It is a flowchart explaining the process which the controller 40 performs. It is a flowchart which shows a process at the time of an engine stop. It is a flowchart which shows an engine starting start process. It is a flowchart which shows an engine starting process. It is a flowchart which shows an engine starting start process. It is a flowchart which shows an engine starting start process.

Explanation of symbols

DESCRIPTION OF SYMBOLS 100 FF engine 20 Exhaust passage 30 Fuel tank 32 Fuel gallery 33 Injector 40 Controller 41 Fuel supply gun sensor (fuel supply determination means)
42 Air-fuel ratio sensor (first alcohol content rate detection means)
44 Alcohol sensor (second alcohol content rate detection means)
S121 Alcohol content rate storage means before engine stop S162 Fuel switching determination means S221 Alcohol content rate storage means before engine stop

Claims (13)

A variable compression ratio control device that variably controls the compression ratio of an engine that can use gasoline containing alcohol,
First alcohol content detection means provided in an exhaust passage of the engine for detecting the alcohol content of gasoline used during engine operation;
An alcohol content before storage stop that stores the alcohol content before engine stop detected by the first alcohol content detection means when the engine is stopped;
The engine compression ratio variable control device, wherein the engine compression ratio is set to a higher compression ratio as the alcohol content is higher at the next engine operation. Refueling determination means for determining whether fuel has been refueled in the fuel tank;
Fuel switching determination means for determining whether or not the fuel in the fuel gallery has been switched to the fuel after refueling by engine operation after it has been determined that fueling has been performed by the fueling determination means;
When it is determined at the next engine operation that the fuel in the fuel gallery is not switched to the fuel after refueling, the engine compression ratio is set to a low compression ratio regardless of the alcohol content. The engine compression ratio variable control device according to claim 1. When it is determined that the fuel in the fuel gallery is switched to the fuel after refueling during the next engine operation, the compression ratio of the engine is determined based on the fuel stored by the alcohol content storage unit before stopping the engine. 3. The engine compression ratio variable control device according to claim 2, wherein the engine compression ratio variable control device is set. When the fuel consumption from the last refueling to the present is less than the fuel mass in the pipe from the fuel tank to the injector, the fuel switching determination means determines that the fuel in the fuel gallery is the fuel after refueling. 4. The engine compression ratio variable control apparatus according to claim 2, wherein it is determined that the engine has not been switched to. 5. The engine compression ratio variable control device according to claim 4, wherein the fuel consumption amount is estimated from an intake air amount into an engine combustion chamber and an air-fuel ratio. 5. The engine compression ratio variable control device according to claim 4, wherein the fuel consumption amount is estimated from a valve opening time of the injector and an engine rotation speed. A second alcohol content detection means provided in the fuel gallery of the engine for detecting the alcohol content of gasoline used during engine operation;
Comparing the alcohol content rate stored by the pre-engine stop alcohol content rate storage means with the alcohol content rate detected by the second alcohol content rate detection means, either fuel is gasoline that does not contain alcohol. 2. The engine compression ratio variable control device according to claim 1, wherein the engine compression ratio is set to a low compression ratio at the next engine operation regardless of the alcohol content. If the fuel whose alcohol content is detected by the second alcohol content detection means contains alcohol, the engine compression ratio is set to a high compression ratio after a predetermined time has elapsed since the engine started. The engine compression ratio variable control device according to claim 7. A second alcohol content detection means provided in the fuel gallery of the engine for detecting the alcohol content of gasoline used during engine operation;
The compression ratio of the engine is set at the next engine operation based on the alcohol content rate stored by the alcohol content rate storage means before the engine stop, and the second alcohol content rate detection means after a predetermined time has elapsed since the engine started. 2. The engine compression ratio variable control device according to claim 1, wherein the engine compression ratio is set based on the detected alcohol content. 10. The engine compression ratio variable control according to claim 8 or 9, wherein the predetermined time is a time required for consuming the fuel before refueling remaining at the tip in the fuel gallery by engine operation. apparatus. The engine compression ratio according to any one of claims 7 to 10, wherein the second alcohol content rate detection means determines that the alcohol content rate is higher as the alcohol concentration in the fuel is higher. Variable control device. The engine according to any one of claims 7 to 11, further comprising key insertion detecting means for detecting a key-in signal from the key box, and starting the compression ratio variable control together with the detection of the key-in signal. Variable compression ratio control device. The engine compression ratio according to any one of claims 1 to 12, wherein the first alcohol content rate detection means determines that the leaner the exhaust air-fuel ratio, the higher the alcohol content rate. Variable control device.

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